Production of aromatics-rich gasoline with low benzene content

Abstract

A process is disclosed for the production of high octane gasoline rich in aromatics but containing a relatively low concentration of benzene. The process comprises the separation of C 6 fraction of the gasoline feedstock into n-hexane and C 6 isomers. The n-hexane and C 7 + streams are catalytically reformed to produce a reformate with a diminished yield of benzene. The reformate is separated and the C 6 - reformate fraction containing benzene is alkylated employing acidic metallosilicate catalyst such as ZSM-5 as the catalyst and preferably methano or propylene as the alkylating agent. The alkylate comprises C 7+ alkylaromatics. The C 6 isomers are blended into the gasoline pool.

What is claimed is: 
     
       1. A fixed bed process for the alkylation of reformate comprising C 6-  hydrocarbons to produce high octane gasoline, comprising; (a) separating a naphtha feedstream by fractionation into a lower boiling fraction comprising iso-C 6  aliphatic hydrocarbon components and a reformer feedstock fraction comprising higher boiling C 6+  aliphatic hydrocarbon components;   (b) reforming the reformer feedstock fraction comprising the higher boiling C 6+  aliphatic components in contact with reforming catalyst and under reforming conditions to produce a reformate containing benzene and C 7+  hydrocarbons;   (c) separating said reformate into a C 6-  hydrocarbon stream containing benzene and paraffins and a C 7+  hydrocarbon stream;   (d) introducing said C 6-  hydrocarbon stream and alkylating agent into an alkylating zone in contact with acidic metallosilicate catalyst under alkylating conditions whereby benzene is alkylated to produce high octane gasoline containing C 7+  aromatic hydrocarbons.   
     
     
       2. The process of claim 1 wherein said C 6+  hydrocarbon feedstock comprises n-hexane fraction from a de-isohexanizer C 6  hydrocarbon feedstock splitter. 
     
     
       3. The process of claim 1 wherein said alkylating agent is taken from the group comprising light olefins, lower alkanol and fuel gas containing light olefins. 
     
     
       4. The process of claim 3 wherein said light olefins comprise propylene and said lower alkanol comprises methanol. 
     
     
       5. The process of claim 1 wherein said reformate is separated in a fractionator to produce said C 6-  hydrocarbon stream. 
     
     
       6. The process of claim 1 wherein said metallosilicate catalyst comprises acidic, shape-selective aluminosilicate zeolite. 
     
     
       7. The process of claim 6 wherein said zeolite comprises ZSM-5. 
     
     
       8. A process for the conversion of C 6  hydrocarbons into high octane aromatics-rich gasoline containing a reduced amount of benzene, comprising; (a) separating by fractionation a feedstock comprising C 6  hydrocarbons into a first, higher boiling fraction comprising n-hexane and a second, lower boiling fraction comprising iso-hexane in a de-isohexanizer fractionator;   (b) introducing said first, higher boiling n-hexane fraction to a hydrocarbons reforming zone in contact with reforming catalyst under reforming conditions whereby reformate is produced containing a reduced amount of benzene;   (c) separating said reformate into a C 7-  hydrocarbon stream containing benzene and paraffins and a C 7+  hydrocarbon stream;   (d) introducing at least a portion of said C 7-  hydrocarbon stream and alkylating agent into an alkylating zone in contact with acidic metallosilicate catalyst under alkylating conditions whereby benzene is alkylated to produce high octane gasoline containing C 7+  aromatic hydrocarbons.   
     
     
       9. The process of claim 8 wherein said alkylating agent is taken from the group comprising light olefins, lower alkanol and fuel gas containing light olefins. 
     
     
       10. The process of claim 9 wherein said light olefins comprise propylene and said lower alkanol comprises methanol. 
     
     
       11. The process of claim 8 wherein said reformate is separated in a fractionator to produce said C 7-  hydrocarbon stream. 
     
     
       12. The process of claim 8 wherein said metallosilicate catalyst comprises acidic, shape-selective aluminosilicate zeolite. 
     
     
       13. The process of claim 12 wherein said zeolite comprises ZSM-5. 
     
     
       14. The process of claim 8 wherein step (a) iso-hexane fraction is combined with step (d) high octane gasoline.